Valley printing and embossing techniques used in the manufacture of flooring material formed of thermoplastic sheets and the like are quite well known. However, in the past, such techniques required the use of separate and distinct inks for each and every color of a multi-color pattern or design to be transferred from an embossing and printing roll to the sheet material. Each of such inks required its own container and reservoir. In addition, individual rubber pattern rolls, capable of transferring ink to the desired areas of the embossing and printing roll, and individual annolox rolls to pick up ink from the reservoirs and apply such ink to the pattern rolls were also required for each color ink. Moreover, it was considered essential to keep the different color inks separated on the embossing and printing roll to avoid contaminating the ink reservoirs with other colors used in the design by the reverse pick-up of one color ink by a pattern roll for another color ink. Accordingly, the colors printed on the embossed sheets were separated in the design by at least an eighth of an inch, since the cost of engraving the various rolls to provide for a closer disposition of the different colors was prohibitive. Because of this deficiency, the designs and decorative patterns that could be utilized in the manufacture of flooring material were often limited, and in those cases where the designs sought to simulate bricks, ceramic tiles and other designs requiring various shades and colors, the resultant flooring material often lacked realism. Similarly, the size and cost of the prior embossing and printing equipment increased significantly with the addition of each color, due to the difficulty in maintaining proper inks separation and the necessity to provide for the transfer and feeding of each ink from its respective source to the embossing and printing roll. As a result, equipment to emboss and print more than two or three colors became so complex and costly so as to render such equipment quite impractical for manufacturing flooring material on a mass production basis.
To overcome these deficiencies in the valley printing and embossing techniques heretofore employed, attempts have been made to print additional colors by first printing one or two colors on a sheet of flooring material by conventional valley printing techniques and then superimposing over the previously printed material additional color inks applied by means of further valley printing rolls. However, such techniques have also proved to be quite impractical since it is quite difficult to keep two or more embossing and printing rolls in perfect registration with one another and the sheet material during the sequential printing process. Moreover, to accomplish this technique, a special transparent ink to be superimposed over the prior printed portions is required. The transparency of the top ink permits the prior printed underlayer of ink to show through and thereby form the illusion of a further color. Accordingly, the additional colors printed in this manner often have a poor appearance.